Most commonly, in vitro diagnostic assays that use a liquid suspension of a solid phase support such as particles, for example, paramagnetic particles require a homogeneous suspension of such particles to be useful in the diagnostic assay. These particles tend to settle to the bottom of a container when the container holding the particles is stored in an upright, non-moving position. The particles require mixing to bring them back to liquid homogeneous suspension before the particles can be used in a diagnostic assay.
Commonly used mixers in automated clinical analyzers typically consist of rotors for generating rotary movement of the particle container or rotary movement of an element within the particle container for a given period of time before the particles in the container may be sampled for use in a diagnostic assay. Mixing to resuspend the particles during the rotary movement is commonly aided by turbulence in the container generated by frequent changes of direction of the rotary movement and by the internal design of the container itself.
Presently, known mixers used in automated clinical analyzers fail to achieve complete resuspension and homogenization of particles. A common cause for this failure arises from the difficulty in disrupting interactions formed by the coated particles. These interactions will occur more frequently when the particles have settled to the bottom of their container. Such interactions are commonly due to electrostatic and hydrophobic interactions, either between the surface of the particles or between the surface of the particles and the walls of the container. Small aggregates of particles formed due to these interactions are particularly difficult to disrupt using solely rotary movement of the container.
An improved mixing system for rapidly and thoroughly resuspending and homogenizing coated particles useful as the solid phase support component in in vitro diagnostic assays is needed.